Of all appendiceal cancers, the most mutated genes are reported in mucinous neoplasms of the appendix, not including those in the RAS–RAF–MEK–ERK signaling pathway, followed by low-grade appendiceal mucinous neoplasms, appendiceal goblet cell adenocarcinomas, and mucinous adenocarcinomas of the appendix, in which this signaling pathway is most frequently affected, showing its importance in their tumorigenesis. The gene discussed is MAPK1; the disease is goblet cell carcinoma.